Preheat the oven to 200ºC/180ºC fan and grease and line a 32 x 22cm (12½ x 8½in) Swiss roll tin with parchment paper.

Add the eggs and sugar to a bowl, and whisk for about 5 minutes on a medium-high speed, until the mixture is paler, and mousse-like. Sift the flour and cocoa powder into the bowl, and add the vanilla extract. Carefully fold the ingredients together until the mixture is combined. Pour into the Swiss roll tin and smooth over. Bake in the oven for 10 minutes.

Once baked, remove from the oven. Take another piece of parchment paper and dust with icing sugar. Flip the Swiss roll onto the sugar-covered paper. Carefully remove the original piece of parchment paper that was in the tin and fold the sponge up from short side to short side quite tightly (be careful, it will be very hot!). Leave to cool fully, all rolled up.

Filling
Beat the butter in a bowl on its own until smooth. Add the icing sugar and cherry conserve and mix together until combined.

Ganache
Add the dark chocolate to a heatproof bowl. Heat the double cream in a small pan until just before boiling point. Pour the hot cream over the chocolate and leave to sit for at least 5 minutes. Stir to combine until melted and smooth. Let the ganache sit in the fridge for 30–45 minutes, covered, then whip with an electric whisk until smooth and fluffy.

Assembly
Carefully unroll the sponge and spread the buttercream over it. Sprinkle on the cherries, then re-roll into a log shape. Slather the ganache over the outside of the cake, and use a fork or skewer to create a bark look! Or, pipe the ganache on instead.